This is an intriguing project you've got here — clearly, there's utility in what you've built. I'd like to offer some constructive insights as a UI & UX designer.
Header: Consider refining the top nav. Placing the title/logo to the left and the notification icon alongside buttons on the top-right creates a sense of spatial balance. Shrinking the search field and centering it would not only economize space but also mitigate the initial impression that it's an intrusive advertisement.
Body: A slight reconfiguration can go a long way. Situate filters to the left and the map to the right to capitalize on users' muscle memory from interacting with similar interfaces. Use Inter (Google Fonts) for a cleaner look. If you want to avoid Google Fonts, just go with Verdana.
User Interaction: Your attempts to clarify map submissions suggest the current UX leaves room for improvement. A single, dedicated 'Submit Location' button leading to a streamlined modal or page can make the process more intuitive. It eliminates the need for repeated explanations scattered throughout the page.
Promotion: The 'Help Us Spread the Word' section risks being mistaken for an ad. Focus on optimizing the core experience; a compelling product naturally invites sharing.
Listing: Optimize space utilization in the list view. Presenting three cards side-by-side allows for easier scanning. Implementing a toggle for card and list views could be a user-friendly addition.
Overall, you've done commendable work. The key lies in fine-tuning the details to make the interface not just functional, but easier to use.